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Nport Component (S-Parameter Files) in PSS Analysis

Frank Wiedmann

The nport component that is used to include S-parameter files in a simulation has been improved very much in MMSIM 12.1 with respect to earlier releases. However, in its current state, it unfortunately cannot be used in a pss analysis (see the comments at the end of http://www.cadence.com/Community/blogs/rf/archive/2012/11/19/spectre-rf-mmsim-12-1-preview-of-coming-attractions.aspx ).

It is currently not clear if there is sufficient demand from Cadence customers to implement support for the pss analysis into the nport component in the upcoming MMSIM 13.1 release. So, if you would like to use S-parameter files in a pss analysis in the near future, you might want to ask Cadence support to file a duplicate of CCR 1042280 on your behalf.

  • Tawna

    Hi Frank, just to clarify... 

    Linear and spline interpolation methods are supported in pss-hb and hb (and all subsequent small signal analyses) and envlp. 

    pss-shooting can be used with the nport in some circumstances.  Linear and spline interpolation methods are not supported for Shooting QPSS/QPXX, Shooting autonomous PSS/PXX, and Shooting Envlp.

     Things have been rapidly improving with the nport - when I have an update, I'll be sure to report it.

    And I fully agree - if enhancements are desired, make sure to contact Cadence Customer Support and request an Enhancement CCR.

     

    best regards,

    Tawna

  • Tawna

    One more thing...where spline and linear interpolation are not supported, rational interpolation is supported.

     

    Best regards,

    Tawna

  • Frank Wiedmann
    Hi Tawna,

    Thanks for your clarification. Unfortunately, rational interpolation does not work very well in many cases. The resulting models are often not passive so that the simulation will blow up. You yourself recommend to be careful with this setting on page 16 of the application note at http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:DocumentViewer;src=wp;q=ApplicationNotes/Custom_IC_Design/NportAppNote11.1.pdf and in the comments to http://www.cadence.com/Community/blogs/rf/archive/2011/03/23/my-favorite-nport-settings.aspx .

    I would also like to point out that not only the pss analysis of autonomous circuits (oscillators) is not supported with the nport component, but also the pss analysis of driven circuits. Our testcase that is referenced by the CCR is a driven circuit.

    Best regards,

    Frank                                         
  • Tawna

    Hi Frank,

    As I've mentioned in my postings before, I typically don't recommend rational interpolation.  However, there are times that it's required.

    Rational interpolation can be a reasonable choice if you have lumped elements.  However, the rational model is not as robust and accurate as the convolution based model (linear or spline), particularly when the s-parameter data models distributed systems with long propagation delay, or the DUT is a multi-port system with the number of ports > 4.

    We are aware of your desire for improved nport performance/support with the Shooting Newton engine and I'm glad that you filed an enhancement CCR requesting improved nport functionality.

    Best regards,

    Tawna

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